Book contents
- Frontmatter
- Dedication
- Contents
- Preface
- Part I Condensed Matter Physics
- Part II Quantum Field Theory
- Part III Quantum Field Theory Approach to Condensed Matter Systems
- 13 Quantum Field Theory Methods in Condensed Matter
- 14 Metals, Fermi Liquids, Mott and Anderson Insulators
- 15 The Dynamics of Polarons
- 16 Polyacetylene
- 17 The Kondo Effect
- 18 Quantum Magnets in 1D: Fermionization, Bosonization, Coulomb Gases and “All That”
- 19 Quantum Magnets in 2D: Nonlinear Sigma Model, CP1 and “All That”
- 20 The Spin-Fermion System: a Quantum Field Theory Approach
- 21 The Spin Glass
- 22 Quantum Field Theory Approach to Superfluidity
- 23 Quantum Field Theory Approach to Superconductivity
- 24 The Cuprate High-Temperature Superconductors
- 25 The Pnictides: Iron-Based Superconductors
- 26 The Quantum Hall Effect
- 27 Graphene
- 28 Silicene and Transition Metal Dichalcogenides
- 29 Topological Insulators
- 30 Non-Abelian Statistics and Quantum Computation
- Further Reading
- References
- Index
16 - Polyacetylene
from Part III - Quantum Field Theory Approach to Condensed Matter Systems
Published online by Cambridge University Press: 25 October 2017
- Frontmatter
- Dedication
- Contents
- Preface
- Part I Condensed Matter Physics
- Part II Quantum Field Theory
- Part III Quantum Field Theory Approach to Condensed Matter Systems
- 13 Quantum Field Theory Methods in Condensed Matter
- 14 Metals, Fermi Liquids, Mott and Anderson Insulators
- 15 The Dynamics of Polarons
- 16 Polyacetylene
- 17 The Kondo Effect
- 18 Quantum Magnets in 1D: Fermionization, Bosonization, Coulomb Gases and “All That”
- 19 Quantum Magnets in 2D: Nonlinear Sigma Model, CP1 and “All That”
- 20 The Spin-Fermion System: a Quantum Field Theory Approach
- 21 The Spin Glass
- 22 Quantum Field Theory Approach to Superfluidity
- 23 Quantum Field Theory Approach to Superconductivity
- 24 The Cuprate High-Temperature Superconductors
- 25 The Pnictides: Iron-Based Superconductors
- 26 The Quantum Hall Effect
- 27 Graphene
- 28 Silicene and Transition Metal Dichalcogenides
- 29 Topological Insulators
- 30 Non-Abelian Statistics and Quantum Computation
- Further Reading
- References
- Index
Summary
Carbon has four electrons in its outer electronic shell, which contains one s and three p orbitals. This, however, is the picture for an isolated atom. When the carbon atom is part of a material with a given crystal structure, almost invariably, for energetic reasons imposed by geometric constraints associated with the crystal structure of the material, two or more of these orbitals combine in a hybrid form that is a linear combination of the former. This interesting phenomenon is known as hybridization. When the four orbitals combine in the so-called sp3 hybridization, the hybrid orbitals assemble in the form of a tetrahedron, which is the basic building block of diamond. Conversely, when three orbitals, namely, one s and two p, combine to create hybrid sp2 orbitals, these are now co-planar, pointing to directions that make an angle of 120◦ among themselves. An unexpectedly vast and extremely interesting amount of physical phenomena emerge in materials formed by this form of carbon. Among these we find polyacetylene and graphene, respectively, possessing one- and two-dimensional structures.
Polyacetylene is a polymer presenting a sequence of CH radicals, formed by carbon atoms, each one with three sp2 hybridized orbitals having covalent bonds with two adjacent carbon atoms, thus forming a zig-zag chain (transpolyacetylene). The third hybridized orbital of each carbon atom is covalently bonded to a hydrogen atom. There remains a p-orbital, which does not hybridize, which is occupied by a single electron. Since this orbital admits up to two electrons with opposite spins, the carbon p-electrons in polyacetylene can move all over the chain, being therefore responsible for most of the interesting physics of this polymer. Especially interesting effects derive from the interplay of the carbon p-electrons with the lattice, imparticular with deformations thereof possessing nontrivial topological properties and, for this reason, called topological solitons.
Polyacetylene exhibits remarkable effects, such as the Peierls mechanism, induced by the electron-lattice interaction, by which a gap is generated where otherwise there would be a Fermi surface.
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- Quantum Field Theory Approach to Condensed Matter Physics , pp. 261 - 279Publisher: Cambridge University PressPrint publication year: 2017